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KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY, KUMASI
COLLEGE OF SCIENCE
FACULTY OF BIOSCIENCES
DEPARTMENT OF THEORETICAL AND APPLIED BIOLOGY
HELMINTH CONTAMINATION OF LETTUCE AND ASSOCIATED RISK FACTORS AT PRODUCTION SITES, MARKETS, AND STREET FOOD VENDOR SITES IN URBAN AND PERI-URBAN KUMASI.
A THESIS PRESENTED TO THE DEPARTMENT OF THEORETICAL AND APPLIED BIOLOGY, COLLEGE OF SCIENCE, KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY, IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE (ENVIRONMENTAL SCIENCE)
BY
LINDA AURELIA ANDOH
SEPTEMBER 2006
1
DECLARATION
I hereby declare that this thesis presented to the Department of Theoretical and Applied Biology in partial fulfillment for the award of MSc. Degree, is a true account of my own work except for the references that have been duly acknowledged.
Signature…………………………… Date………………………….
NAME: ANDOH LINDA AURELIA
(STUDENT)
Signature…………………………….. Date……………………………
NAME: PROF. R. C. ABAIDOO
(SUPERVISOR)
2
DEDICATION
To my father, Nana Kwantwi Berimah II and Mother, Esther Darko-Kumi
3 ACKNOWLEDGEMENT
To God be the Glory, great things He has done. I wish to acknowledge the time, energy and resources sacrificed by my supervisor, Prof. R.C. Abaidoo and Dr. K. Obiri-Danso of the
Department of Theoretical and Applied Biology for their extensive support, advice, patience and criticisms in making this work what it is, you’ve really been my mentors. Thank you so much.
I am very grateful to the Challenge Program on Water and Food (CPWF) for sponsoring this project.
My sincere and profound gratitude also goes to my parents and family for their support, encouragement and prayers through out my education. To Rev. Martin Ofori, Lise Tonner Klank,
Cindy (DFVF) and Flemming Konradsen (UC) for their motivation, pieces of advice, patience and sacrifices in making this study a reality.
My gratitude also goes to of all the Lecturers of the Department of Theoretical and Applied
Biology, not forgetting Mr. Osei-Tutu and Jimmy. To Auntie Anita and Auntie Eunice, I say thank you for being a pillar of support and for everything.
Finally, to all my friends and course mates especially Fred Amponsah-Doku, Maxwell Akple, Yaw
Amo Sarpong, Kwame Osei Boateng, Augustina Annan Flora Turkson and Betty Agyenim-Boateng for their special assistance.
4 TABLE OF CONTENT
Declaration ii Dedication iii Acknowledgement iv List of Tables x List of Figures xi List of Plates xiii Abstract xiv
CHAPTER ONE 1.0 INTRODUCTION 1 1.1 Background ...... Error! Bookmark not defined. 1.2 Problem Statement ...... Error! Bookmark not defined. 1.3 Research Questions...... Error! Bookmark not defined. 1.4 Objectives of Study...... Error! Bookmark not defined. 1.4.1 General Objectives...... Error! Bookmark not defined. 1.4.2 Specific Objectives ...... Error! Bookmark not defined.
CHAPTER TWO ...... Error! Bookmark not defined. 2.0 LITRETURE REVIEW 2.1 TERMS AND DEFINITIONS...... Error! Bookmark not defined. 2.2 Irrigation in Kumasi ...... Error! Bookmark not defined. 2.3 Sources of contamination of vegetables ...... Error! Bookmark not defined. 2.4 Sources of pathogenic microorganisms on fresh fruits and vegetables Error! Bookmark not defined. 2.4.1 Pre-harvest ...... Error! Bookmark not defined. 2.4.2 Harvest ...... Error! Bookmark not defined. 2.4.3 Post Harvest Sources...... Error! Bookmark not defined. 2.5 Washing and Decontamination ...... Error! Bookmark not defined. 2.6 Use of untreated and partially treated wastewater for irrigation...... Error! Bookmark not defined. 2.7 Health Risks ...... Error! Bookmark not defined. 2.8 Wastewater use guidelines...... Error! Bookmark not defined. 2.9 Pathogens and Parasites in wastewater ...... Error! Bookmark not defined.
CHAPTER THREE...... Error! Bookmark not defined. 3.0 MATERIALS AND METHODS...... Error! Bookmark not defined. 3.1 Study Area...... Error! Bookmark not defined. 3.2 Research Methods...... Error! Bookmark not defined. 3.2.1 Sampling Sites...... Error! Bookmark not defined. 3.2.1.1 Production sites...... Error! Bookmark not defined. 3.2.1.2 Market sites...... Error! Bookmark not defined. 3.2.1.3 Street food vendors ...... Error! Bookmark not defined. 3.2.2 Sampling ...... Error! Bookmark not defined. 3.2.2.1 Lettuce sampling from Production site ...... Error! Bookmark not defined. 3.2.2.2 Market site...... Error! Bookmark not defined. 3.2.2.3 Street food vendors ...... Error! Bookmark not defined. 3.2.2.4 Irrigation/Refreshing water sampling ...... Error! Bookmark not defined. 3.2.3 Preparation of samples and Quantification of Helminth eggs/larvaeError! Bookmark not defined. 3.2.4 Identification of Helminth eggs ...... Error! Bookmark not defined.
5 3.2.5 Health Risk Assessment and Perception...... Error! Bookmark not defined. 3.3 Statistical Analysis...... Error! Bookmark not defined. 4.0 RESULTS ...... Error! Bookmark not defined. 4.1 Helminth eggs in irrigation water and lettuce at production Site ...... Error! Bookmark not defined. 4.2 Helminth eggs in lettuce and refreshing water at Market SiteError! Bookmark not defined. 4.3 Relationship between helminth eggs/larvae counts in irrigation water Error! Bookmark not defined. farm lettuce, refreshing water and market lettuce ...... Error! Bookmark not defined. 4.4 Helminth Numbers at Street Food Vendor Sites...... Error! Bookmark not defined. 4.5 Health Risk Assessment...... Error! Bookmark not defined. 4.5.1 Production Site...... Error! Bookmark not defined. 4.5.2 Market Site...... Error! Bookmark not defined. 4.5.3 Street Food Vendor Sites ...... Error! Bookmark not defined.
CHAPTER FIVE ...... Error! Bookmark not defined. 5.0 DICUSSION, CONCLUSION AND RECOMMENDATION ...... Error! Bookmark not defined. 5.1 DISCUSSION ...... Error! Bookmark not defined. 5.1.1 Contamination of irrigation water and lettuce at Production(Farm) Sites...... Error! Bookmark not defined. 5.1.2 Contamination of lettuce at Market Sites...... Error! Bookmark not defined. 5.1.3 Contamination at Street Food Vendor Sites...... Error! Bookmark not defined. 5.1.4 Health Risk...... Error! Bookmark not defined. 5.2 CONCLUSION...... Error! Bookmark not defined. 5.3 RECOMMENDATIONS...... Error! Bookmark not defined. Table 2.1 Health risk from use of wastewater in agriculture. .... Error! Bookmark not defined. Table 2.2 Recommended microbiological quality guidelines for treated wastewater used for crop irrigation...... Error! Bookmark not defined. Table 2.3 Survival times of selected excreted pathogens (helminthes) on crops...... Error! Bookmark not defined. Table 4.4 Mean number and types of helminth eggs on lettuce leaves (per 100g) from selected street food vendor sites...... Error! Bookmark not defined.
LIST OF FIGURES ...... Error! Bookmark not defined. Figure 2.1 Life Cycles and Transmission of Hookworm ...... Error! Bookmark not defined. Figure 2.2 Life cycle and Transmission of Ascaris lumbricoidesError! Bookmark not defined. Figure 3.1 Map showing Kumasi in relation to the rest of Ghana...... Error! Bookmark not defined. Figure 3.2 Map showing Urban/peri-urban Farm sites in Kumasi and the Selected farms for the study Error! Bookmark not defined. Figure 4.1 Helminth egg in irrigation water from the farm sites. Error! Bookmark not defined. Figure 4.2 Helminth eggs on Lettuce samples from the farms sites ...... Error! Bookmark not defined. Figure 4.4 Helminth eggs/larvae on lettuce samples from the market sites..... Error! Bookmark not defined. Figure 4.6 Mean total count of helminth eggs on lettuce leaves and in refreshing water....Error! Bookmark not defined. Figure 4.7 Total helminth egg count on lettuce leaves on farm and their corresponding markets Error! Bookmark not defined. Figure 4.8 Types of sanitizing solutions used by street food vendors for washing lettuce..Error! Bookmark not defined.
6
LIST OF PLATES ...... Error! Bookmark not defined. Plate 3.1 A portion of the Kakari site with some areas developed for residential use 38....Error! Bookmark not defined. Plate 3.2a Sections of the Badu farm site 39 ...... Error! Bookmark not defined. Plate 3.2 b Section of the Badu farm site 40...... Error! Bookmark not defined. Plate 3.3 A section of the Deduako farm site 41...... Error! Bookmark not defined. Plate 3.4 Sampling of lettuce from a Bed at Badu’s Farm (Site 2) 43.....Error! Bookmark not defined. Plate 4.1 Larvae of Strongyloides stercoralis 50 ...... Error! Bookmark not defined. Plate 4.4 Farmers working without Personal Protective Equipment 62 ...Error! Bookmark not defined.
7 ABSTRACT
In the urban cities of many developing countries demand for fresh vegetables has necessitated the use of wastewater for irrigation. Microbial load on these vegetables at both the production and the distribution points is reportedly high. The study assessed the helminth parasites contamination on lettuce and associated risk factors at farm, market and the fast food street vendor points in Kumasi.
Three farms, three market sites where lettuce from the selected farms is sold and thirteen street food vendors who purchase their lettuce from these markets were studied. Samples of lettuce, irrigation water and refreshing water (water used in keeping lettuce fresh throughout the day) were collected from these sites and analyzed for helminth eggs using standard methodology (Schwartzbrod, 1998).
Helminth eggs on lettuce leaves, irrigation water and refreshing water on the farms and markets were mostly Ascaris lumbricoides with others being Shistosoma, Hookworm, Trichuris trichura,
Taenia, Clonorchis and Strongyloides larvae. Helminth eggs on lettuce ranged between 4 and 14 eggs/100g wet weight and 3 and 25 eggs/l in irrigation water on the farms, and between 2 and 7 eggs/100g wet weight and 4 to 15 eggs/l in refreshing water on the markets. Helminth egg counts on lettuce leaves on two farms were 25-36% more compared to the farms irrigation water but one farm had 25% more in irrigation water compared to the lettuce leaves. Helminthes eggs on two farms lettuce were 33.3% and 42.9% higher compared to the corresponding markets samples but 10.5% higher one market compared to its farm source. Helminth eggs in street food lettuce samples analysed from the selected areas were only Ascaris and Shistosoma eggs ranging between 0 to
2eggs/100g wet weight. Helminth egg numbers for both farm and market samples exceeded the recommended level of <1egg l-1 (WHO, 1989). Education on farm practices, post harvest handling and washing methods at both market and street food vendor sites and improved hygienic practices at consumer level will help reduce their numbers and minimize the risk.
8 CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND
The use of wastewater for irrigation in agriculture has been practiced for many years in arid zones of industrialized as well as developing countries. The persistence in the use of this water resource has been attributed to several factors, including the decreasing availability of water resources for irrigation as a result of the increasing demand for potable water in urban and peri-urban communities, the high cost of artificial fertilizers and the realization that nutrients in wastewater can increase crop production and the social acceptance of the practice (Mara and Cairncross, 1991).
For the Ghanaian economy, agriculture contributes 36.6% of the gross domestic product (GDP) and employs 60% of the labour force. The average annual per capita income of those employed in agriculture is estimated at US$390 ( CIA World Fact Book, 2005).Irrigated agriculture is therefore important in peri-urban communities producing about 90 % of vegetables consumed in the cities and also providing a major source of income for the households (Drechsel et al., 2001). The growing demand for fresh and perishable agricultural produce in the major cities is driving the development of peri-urban agriculture. This demand is not seasonal as vegetable farming is done all year round. The vegetables commonly grown include cabbage (Brassica oleracea capitata), spring onions (Allium fistulosum), carrots (Daucus carota ssp.sativus), tomato (Lycopersicon esculentum), onion (Allium cepa), Shallots (Allium escalonicum), egg plant (Solanum melongena) local spinach
(Amaranthus spp), cucumber (Cucumis sativa) and lettuce (Lactuca sativa) which is eaten raw
(Sanduri, 2004).
It has been reported that vegetables can be contaminated by microrganisms at both the production and the distribution points (Drechsel et al., 2000) and this has been attributed to the irrigation water, sources of crop nutrients (organic manure) and handling and storing of produce at points of sale.
9
Wastewater reuse may therefore lead to public health risks of transmission of enteric diseases following the consumption of raw vegetables. These include waterborne and foodborne transmission of helminths, particularly nematodes and endemic parasitic diseases to which children are most vulnerable (HCWC, 1994; Shuval et al., 1986). Pathogenic bacteria such as Escherichia coli and Salmonella have also been implicated (Sonou, 2001).
1.2 PROBLEM STATEMENT
The use of polluted and or marginal quality water for irrigating vegetables has been done for ages.
These irrigation water sources are known to be contaminated and in most cases exceed the WHO guidelines significantly (Keraita et al., 2003b)
Some researchers have shown that in the production-consumer pathway of lettuce, markets form an important aspect. Sellers mainly women buy them on-farm from field beds that have been ordered in advance and transport them to these markets where they are sold in bulk or retailed to consumers
(Danso and Drechsel, 2003). According to Drechsel et al (2000), as consumers demand fresh and clean but not safe vegetables, refreshing and cleaning with water often of as bad quality as irrigation water is thus the normal practice in markets. It has been documented by Drechsel et al (2000) that it is difficult to find on markets, any irrigated vegetables (lettuce, spring onions, and cabbage) which are not contaminated with faecal coliforms and helminths eggs. It is therefore hypothesised that the contamination of lettuce sold in markets is significant and higher than its contamination on arrival from the farm.
The rapid growth of the urban population (2.7%) and the increasing number of working people have caused changes in the eating habits of Ghanaians (Ghana Statistical Service, 2002). Consequently, fewer people, especially in the urban areas, are eating home-cooked meals as much food is
10 purchased from vendors of the fast-food industry which is also growing rapidly. A mini-census and a survey by the National Resources Institute of 334 street vendors in Accra, Ghana indicated that the street food sector employs over 60,000 people and has an estimated annual turnover of over
US$100 million (FAO, 2005). Despite the contributions of street foods to food security and local economies, several outbreaks of foodborne diseases have been traced to the consumption of contaminated street foods which in most cases come with lettuce as part of the salads. Numerous studies have been documented on the potential contamination of street foods by pathogenic microorganisms but the source and contribution of helminth parasites to this contamination is not very clear.
1.3 RESEARCH QUESTIONS:
1. What is the quality of the irrigation water used in lettuce production in urban and peri-urban
Kumasi?
2. What is the quality of the lettuce sold in the market compared to those on farm in terms of
Helminth numbers?
3. What is the quality of the lettuce sold at the street food vendor sites compared to those at the
market and the farm?
4. What are the key risk factors associated with human health, including those related to
hygienic conditions and practices of producers, sellers and consumers of waste water
irrigated lettuce?
1.4 OBJECTIVES OF STUDY
1.4.1 General Objectives
This study will focus on the contamination of lettuce (which is normally consumed raw and perhaps the most perishable of all the vegetables cultivated and sold in most cities in Ghana.) and associated risk factors at production sites, in markets and street food vendors in urban and peri-urban Kumasi.
11
1.4.2 Specific Objectives
1. To assess the microbial quality of irrigation water in relation to helminths eggs
contamination.
2. To assess contamination levels of helminth parasites in lettuce at selected farm sites,
markets and street vendors in urban /peri-urban Kumasi
3. To identify risk factors associated with faecal contamination of lettuce at farm sites, markets
and street food vendors.
4. To develop interventions to reduce the risks of faecal contamination of lettuce.
12 CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 TERMS AND DEFINITIONS
The following paragraphs give working definitions of different terms used in this work.
In many developing urban areas, wastewater is generally a mixture of the three different categories and its use is mainly informal. The uncontrolled and varied nature of sources of wastewater used for irrigation makes it difficult to define, monitor and control the practice. Van der Hoek, (2004) classifies wastewater use into:
• Direct Use- the planned use of raw or treated wastewater where control exists over the
conveyance of the wastewater from the point of collection or discharge from treatment
works to a controlled area where it is used for irrigation. This is the situation pertaining in
most developed nations where physical and institutional infrastructure is well established to
monitor and control the quality of the water and the area where it is used for irrigation.
• Indirect Use- the situation found in many developing countries where much municipal and
industrial wastewater is discharged without treatment, monitoring or control into the water
courses draining an urban area. The resulting water quality varies.
Cornish el al., (1999) classified wastewater as: a. Raw/Untreated Wastewater- liquid discharged from homes or commercial premises to individual systems or municipal sewers. It is a mixture of domestic sewerage- dirty water, human excreta and municipal waste water. It may not contain substantial quantities of industrial effluent. b. Treated /partially treated wastewater- wastewater that has been treated by a natural or artificial purification process to improve its physical, chemical or bacteriological quality before discharge into a surface water body. It may still pose a threat to receiving environments.
13 c. Industrial Effluent - wastewater from industrial processes and containing high levels of heavy metals or other chemicals or organic constituents. Industrial effluent does not normally contain high levels of microbial pollutants.
Wastewater is also categorized according to its origin. The categories include:
1. Grey water: composed of domestic water without urine and faeces
2. Black water: composed of domestic water that is mixed with faeces and urine.
3. Industrial wastewater: composed of water from industrial processes which may contain varying concentration of heavy metals.
Marginal Quality - this term refers to water which is ‘marginal’ for use in agriculture. Abbott and
Hasnip (1997) define it as “water which might pose a threat to sustainable agriculture and or human health by virtue of its quality but which can be used safely for irrigation provided certain precautions are taken”. It describes water, which has been polluted as a consequence of mixing with wastewater or agricultural drainage.
2.2 IRRIGATION IN KUMASI
Kumasi has a semi humid, tropical climate with a total average rainfall of 1340mm. approximately
90% of the annual total falls between March and October. Natural drainage runs from north to south. The principal streams in the area are the Daban, Subin, Aboabo, Sisa and Wiwi. These converge into the Sisa which flows into the Oda River about 9 km south of Kumasi. Small scale irrigated agriculture is done in the dry season in many villages within 40km radius of Kumasi. In other areas, farmers draw water either from ephemeral streams which flow from a series of pools in the dry season or from shallow hand-dug wells. Farmers’ postulate that water drawn from shallow wells are is better in quality than that from the rivers.
14 2.3 SOURCES OF CONTAMINATION OF VEGETABLES
Parasites contaminate crops through various routes taken during pre-harvest, harvest and post- harvest for example, via water contaminated by faeces that are used for irrigation or spraying of crops, by poor personal hygiene practices among handlers of crops, by contact with contaminated soil or by contact with faeces of wild animals. Thus, pathogens from the human and animal reservoir as well as other pathogens from the environment can be found on crops at the time of consumption.
2.4 Sources of pathogenic microorganisms on fresh fruits and vegetables
Adapted from Beauchat and Ryu (1997)
Pre-harvest Post harvest Sorting, packing and further processing equipment • Feces • Feces • Ice • Soil • Human handling • Transport vehicles • Irrigation water (workers, consumers) • Improper storage • Water used to apply • Harvesting equipment (temperature, physical • fungicides, • Transport containers environment) • insecticides (field to packing shed) • Improper packaging • Green or inadequately • Wild and domestic (including new packaging composted manure animals (including fowl technologies) • Air (dust) and reptiles) • Cross-contamination (order • Wild and domestic • Insects foods in storage, preparation, animals (including • Air (dust) and display areas) fowl and reptiles) • Wash and rinse water • Improper display temperature • Insects • Improper handling after Human handling wholesale or retail purchase
2.4.1 Pre-harvest
Soil
In the preparation of soil for planting, farmers mostly use uncomposted organic manures to fertilize the soil. These manures contain several microorganisms (Behrsing et al, 2000). Soil is known to be a rich source of a variety of microorganisms and the non-pathogenic flora is important for the mineralization of plants and animals after their death in the environment.
15 Pathogenic organisms from the human/ animal reservoir can be found in the soil due to irrigation and fertilization with manure and sludge or due to droppings of animals in the farming area. Tissue degrading properties of this flora contaminating vegetables may cause damage during transport and storage of products thereby exposing them to further microbial attack.
Irrigation Water
Water is mainly used for irrigation of plants and its quality varies depending on whether it is surface water or potable water. A recent study of two sites in the Accra Metropolitan Area (Sonou M. et al,
2001) revealed that wastewater was the most frequently used water for irrigation purposes. As much as 60% of the farmers interviewed at Dzowulu Power Pool Station (67.7%) and at Castle Parks and
Gardens (32.3%) confirmed the use of this type of water. Less than a quarter (23.3%) use pipe- borne water while approximately 17% use piped water stored in a ground reservoir.
Irrigation water may be a source of contaminating microorganisms. Surface water from streams and lakes may be contaminated with pathogenic protozoa, bacteria and viruses. The occurrence of L. monocytogenes, Salmonella and viruses has been reported (Castillo Martín et al., 1994; Nguyen and
Carlin, 1994 and 2000).Water from sewage plants can be used for irrigation purposes but without further hygienic treatment, it may represent a risk for contaminating the crop.
Giardia cysts have been detected on fresh vegetables like carrots, mint, radish and potatoes irrigated with wastewater (Lane and Lloyd, 2002, Amahmid et al, 1999). Of waters used to irrigate vegetables in the USA and several American countries, 60% tested positive for Giardia cysts and
36% tested positive for cryptosporidium oocysts (Thurston-Enriquez et al, 2002).
Organic Fertilizers
In enhancing production of the vegetables there is the need for fertilizers. Inorganic fertilizers are however very expensive hence, the use of organic manure which is inexpensive. Sewerage, manure,
16 slurry, sludge and compost of human and animal origin are commonly used as organic fertilizer for vegetable production particularly in organic production systems. Of all the organic manures however, poultry manure seems to be the cheapest and the most preferred.
In Kumasi, the use of poultry manure is very common due to its high availability and low price (US
$0.1 per sack). Only a few farmers use mineral fertiliser in addition to this (mostly for cabbage production). In urban Kumasi, many more vegetable farmers use mineral fertilisers (US $14 per
50kg NPK) but combine it with poultry manure when possible(Danso et al., 2003).
Usage however of the poultry manure may have its adverse effects just as most inexpensive alternatives do. The faecal origin of these fertilizers, however, indicates a potential risk of contamination by viruses, bacteria and parasites pathogenic to humans.
In Belgium and Finland, Listeria monocytes was found in 6.7 to 20% of the samples analysed
(Husu, 1990; Van Renterghem et al, 1991) and in sewerage sludge (stauch, 1991).
Poultry manure, which represents 75% of the organic fertiliser used, generally contains faecal coliforms (1.30x106/g) and enterococci (3.4x106/g) (Westcot, 1997). This is evident even in situations where pipe-borne water was used for irrigation signifying that the contamination was from the poultry manure. Vegetables cultivated with manure are highly infected by bacteria, indicating contamination from a faecal source (Sonou et al., 1999).
The concentration of microorganisms in animal manures is of major importance because this determines the quantity of bacteria which reaches soils and groundwater.
Helminth and protozoan parasites enter the environment in faeces from the intestinal tract of a wide range of domestic, wild and companion animals used as manure for production.
17
In general, increasing the delay between the application of organic fertilizers and harvest could reduce the occurrence of food borne pathogens on vegetables.
2.4.2 Harvest
Vegetables can become contaminated with pathogenic microorganisms during harvesting through faecal material, human handling, harvesting equipment, transport containers, wild and domestic animals, air, transport vehicles, ice or water (Beuchat, 1995).
In an investigation of several food borne illnesses associated with fresh produce (NACMCF,
1999a), agricultural workers were in many cases the likely source of the pathogen. Lack of suitable sanitary hand-washing facilities in the production area can potentially create a hygienic problem.
Clean, well-designed and maintained equipment is less likely to cause damage to fresh produce and to introduce spoilage and pathogenic microorganisms (Brackett, 1992). Dirty storage facilities and the presence of rodents, birds and insects may increase the risk of contamination with food borne pathogens (FDA, 1998). Finally, harvesting at the appropriate time and keeping the harvested product under controlled environmental conditions will help retard growth of post-harvest spoilage
(Brackett, 1992) and pathogenic microorganisms.
2.4.3 Post Harvest Sources
The fecal-oral route of transmission of pathogens broadens to include workers handling vegetables from the point of removal from the plant through all stages of handling, including preparation at the retail and food service levels and in the home. Traditionally recognized post harvest control points for access of pathogens to whole or cut produce include transport containers and vehicles.
18 Post harvest treatment of vegetables includes handling, storage, transportation, and sorting, packing, cutting, cleaning and further processing equipment. Conditions arise during these practices which lead to cross contamination of the produce from other agricultural materials or from the workers.
Environmental conditions and transportation time also influences the hygienic quality of the produce prior to processing or consumption. Poor handling damages fresh produce, rendering them susceptible to the growth/survival of spoilage and pathogenic microorganisms.
Another main source of microbiological contamination at the market level is poor handling and storing practices of vegetables by market women. Vegetable sellers wash the vegetables in water before selling them. Observation of the storage conditions has, however, revealed that the vegetables are generally exposed and are frequently visited by houseflies and other insects including cockroaches. The common micro-organisms isolated from vegetable samples include E. coli, Pseudomonas, Enterobacter cloacae, Salmonella arizonae (Sonou, 2001). Other organisms
(helminthes and protozoan) identified on vegetables collected from the field and market includes free-living soil nematodes, flagellates and Balantidium coli.
2.5 WASHING AND DECONTAMINATION
Washing of vegetables at harvest removes much of the adhering soil and dirt. However, it could also be a source of microbial contamination. Even where washing is applied, effective washing and decontamination of ready-to eat vegetables is difficult. Refreshing and cleaning vegetables with water often as bad quality as irrigation water is thus normal practice in most markets (Dreschel et al., 2000).
Chlorine is the major compound used for disinfection of fresh produce. During sprouting of seeds chlorine can be used in the water to prevent growth of contaminating microorganisms. Though the effect of disinfectants on contaminants depends on many factors including the concentration used,
19 treatment time, temperature, pH and sensitivity of the target organism(s), the most effective form is hypochlorous acid (HOCl) (Simons and Sanguansri, 1997) and chlorine concentration of 100 ppm is frequently used. However, the use of chlorine does not ensure elimination or even an efficient reduction in pathogen levels. Other substances many be used including organic acids, chlorine dioxide, hydrogen peroxide and ozone (Beuchat, 1998). Organic acids alone, or in combination with chlorine, have been shown in experimental designs to effectively reduce the number of pathogens for example, Yersinia enterocolitica and Listeria monocytogenes in parsley (Karapinar and Gonul,
1992; Zhang and Farber, 1996).
Prevention of contamination at all points of the food chain is preferred over the application of disinfectants.
2.6 USE OF UNTREATED AND PARTIALLY TREATED WASTEWATER FOR IRRIGATION
A number of existing studies have documented the prevalence of high intestinal nematode infections found among farmers and their family members who are in direct contact with wastewater (Krishnamoorti et al, 1973; Shuval et al., 1986; Habbari et al., 1999; Blumenthal and
Peasey). Many of these studies are descriptive and have not tried to quantify relative or attributable risk of infection as a result of the use of untreated wastewater for irrigation. An even smaller number of studies have tried to link exposure to a known intestinal nematode concentration and the risk of human nematode infections (Blumenthal et al, 2000).
The different studies on the use of untreated wastewater in agriculture all show similar outcomes with a clearly increased risk of hookworm and Ascaris infections for adult wastewater farmers. A study of Indian farmers using untreated wastewater showed a more than three-fold increased risk of
Ascaris infections, and a more than two-fold increased risk of hookworm infections as compared to
“regular” farmers (Krishnamoorthi et al, 1973). In Haroonabad, a small town in Pakistan, hookworm prevalence in farmers using wastewater with a nematode egg load of 100 eggs/litre was
20 very high, with 80% of the farmers infected. The study showed a more than four-fold increased risk for wastewater farmers as compared to farmers using regular irrigation water. Ascaris prevalence was found to be low in both wastewater farmers as well as regular farmers and no increased risk was found between both groups. A much lower hookworm prevalence was found in children and no excess risk was found for both Ascaris and hookworm infection when children of wastewater farmers and regular farmers were compared (Feenstra et al, 2000).
A study conducted in the city of Faisalabad in Pakistan where farmers were using untreated wastewater with a mean Ascaris concentration of 142 eggs/litre and a mean hookworm concentration of 558 eggs/litre (Ensink et al., 2004b) showed, as compared to the Haroonabad study, a much lower prevalence of hookworm infection of less than 15% among wastewater users
(Ensink et al., 2004a). The studies in Faisalabad and Haroonabad showed similar outcomes, with an almost six-fold increased risk of hookworm infection in adult farmers, but no additional risk in children. Ascaris infections in both adults and children were low and showed no significant additional risk when compared to regular farmers (Ensink et al., draft).
The findings in Pakistan are in contrast to outcomes of research undertaken in Mexico, where children of wastewater farmers had an over five and twelve fold increased risk of Ascaris infection
(Cifuentes, 1998; Blumenthal et al., 2001). The same studies in Mexico compared Ascaris prevalence in wastewater farmers using untreated (125 nematode eggs/litre) wastewater and wastewater conform (< 1 nematode egg per litre) the 1989 WHO water quality guidelines and showed clearly that with deteriorating water quality the risk of Ascaris infections increased
(Cifuentes, 1998; Peasey, 2000; Blumenthal et al., 2001).
In Mexico wastewater retained in a reservoir before it was used in irrigation resulted in an average nematode concentration of less than 1 nematode egg/litre and was thus of WHO standards. Farmers
21 using this water had similar (low) levels of Ascaris infections, compared with farmers using rain water, though an increased risk of Ascaris infection was found in children of wastewater farmers
(Peasey, 2000 and Blumenthal et al., 2001).
2.7 HEALTH RISKS
A third source of potential contamination is found in the manure used by farmers in the management of soil fertility. According to Sonou et al, (2001), vegetables cultivated with manure are highly infected by bacteria, indicating contamination from a faecal source. Poultry manure, which represents 75% of the organic fertilizer used, generally contains Faecal Coliforms
(1.30.106/g) and Faecal Streptococci (3.4.106/g) (Westcott, 1997). Fresh poultry manure sometimes contains disease causing pathogens that can contaminate produce. Manure from swine and carnivores can contain helminths as well as other bacteria. Studies have shown that about 60% of farmers apply fresh poultry manure directly without composting while 40% heap it for some few weeks or more before use (Drechsel and Kunze, 2001)
The cost of pipe-borne water makes it unaffordable to farmers. The use of untreated wastewater for irrigation has therefore become a widespread practice, with its attendant health hazards .When wastewater is used for irrigation without any treatment the pathogens present are applied to the agricultural land. This poses a potential health risk to people exposed to it, such as field workers and their families, consumers and handlers of wastewater-irrigated crops and people living in the neighborhood, passing the fields frequently. The WHO in 1989 documented that the health hazards associated with direct and indirect wastewater use are of two kinds:
• The rural health and safety problem for those working on the land or living on or near the
land where the water is being used, and
• The risk that contaminated products from the wastewater use area may subsequently infect
humans or animals through consumption or handling of the foodstuff or through secondary
human contamination by consuming foodstuffs from animals that used the area.
22
It has been recorded by the High Council of Water and Climate that wastewater reuse may lead to public health risks of transmission of enteric diseases following consumption of raw vegetables. It may also result in the transmission of endemic parasitic diseases that mostly strike children.
Studies have showed that the nutrients and microbiological contaminants in irrigation water sources, in most cases exceed the WHO guidelines significantly (Keraita et al., 2003b). However, according to the World Health Organization, (WHO, 1989) the actual health risks (which is the risk of people falling ill) is lower than the potential health risk. The potential health risk is based on the number of pathogens in the wastewater, while the actual health risk depends on three more factors:
• The time pathogens survive in water or soil
• The dose in which pathogens are infective to a human host
• Host immunity for pathogens circulating in the environment.
The actual risks to public health that may occur through wastewater use can be divided into three broad categories, namely:-
• Those affecting consumers of the crops grown with wastewater (consumer risk),
• Those affecting the agricultural and pond workers who are exposed to the wastewater
(worker risk) and
• Those affecting populations living near the wastewater use scheme (nearby population risk)
(Strauss et al, 1990)
Farmers rarely wear protective clothing or take any protective measures when applying water, or pesticides for that matter. Some are aware of such measures but cannot afford them or give them little priority. No extension services are offered to farmers on irrigation practices, related protection, etc.
23
24 Table 2.1 Health risk from use of wastewater in agriculture
Type of pathogen/infection Relative excess of frequency of infection or disease ______
Intestinal nematode infections (Ascaris lumbricoides, Trichuris Trichura, hookworm) High Bacterial infections Bacterial diarrheas (E.g. cholera, typhoid) Lower Viruses Viral diarrheas Hepatitis A Lowest
Source: World Health Organization 1989
The highest health risk is theoretically for helminth infections. Compared with other pathogens, helminths persist for long periods in the environment from a few months up to 30 years. Host immunity ranges from low to non-existent and the infective dose is small. The typical pattern of infection is one of the chronic rather than transient illnesses, with gradual increase in “worm load”
(Strauss et al, 1990)
In Eritrea, the assessment of the health impacts of raw domestic sewage for vegetable cultivation showed heavy contamination of vegetables by fecal coliforms and Giardia cysts as well as other pathogenic bacteria such as Shigella and Salmonella. (Srikanth et al, 2004). It is known that dietary intake of raw greens (lettuce, cabbage) grown on the raw sewage appears to cause giardiasis, amebiasis, and diarrhoea in the farming community as well as in the surrounding area. Studies of wastewater usage in different parts of the world reveal various gastrointestinal problems in farming communities who are involved in this practice (Cifuentes et al, 1993). In addition to the risk of
25 contamination by direct exposure, consumption of undercooked/ raw vegetables also poses a risk to health (Kowal et al, 1985).
The negative effects of this practice may include microbial contamination of the produce, health hazards to community residents consuming vegetables and raw salad greens, and occupational hazards to farm workers and consumers.
2.8 WASTEWATER USE GUIDELINES
The public health concerns related to wastewater use in agriculture have led to the development of sanitary guidelines that put restrictions on wastewater use according to its pathogen load. Two main
“guideline” schools of thought can currently be distinguished. The American guidelines are based on the principle that there should be no risk as a result of wastewater use; therefore they promote the removal of all pathogenic organisms before wastewater can be used (USEPA, 1992). The World
Health Organisation guidelines are based on the principle of no excess disease in the population using wastewater or consuming produce grown on wastewater (WHO, 1989), and its guidelines are therefore more lenient.
Both approaches have their critics, with the WHO being accused of basing its guidelines on partial studies, ignoring acquired immunity, and measuring with double standards (Shelef, 1991). The
American guidelines though have been accused of being too strict and the wastewater treatment technology to guarantee these standards therefore too expensive. Shuval et al. (1997) estimated that bringing wastewater from WHO to USEPA guidelines would come at the cost of approximately
US$ 3,500,000 – US$ 35,000,000 per prevented case of enteric disease in the exposed community.
The less strict guidelines and the wider range of risk reduction, other than wastewater treatment, make the WHO guidelines more suitable for adoption in developing countries.
26 A first meeting of experts on the use of wastewater in aquaculture and agriculture was held by the
WHO in 1971, which led to the development of the first guidelines (WHO, 1973) and an initial water quality standard of 100 faecal coliforms per 100 ml for crops consumed uncooked. A second meeting in 1987 lead to the inclusion of an intestinal nematode water quality standard (≤ 1 egg/litre) and a revision of the faecal coliform standard for crops eaten uncooked (≤ 1000/100 ml) (WHO,
1989). A review by a group of researchers in 2000, based on existing epidemiological evidence, resulted in a proposal for revision of the 1989 guidelines (Blumenthal et al, 2000) and the need to adopt a stricter nematode guideline value of less then 0.1 eggs/litre (annex 1). However others have suggested the guideline value could be increased to 10 eggs per litre (Ayres et al., 1992). The WHO wastewater irrigation guidelines are currently under review with new guidelines expected in 2004.
The four main measures put forward by the World Health Organization to protect health when wastewater is used are: wastewater treatment, crop restriction, control of wastewater application and human exposure, control and promotion of hygiene (WHO, 1989). Depending on the local sociocultural, institutional and economic conditions, a combination of measures could be selected
Table 2.2 Recommended microbiological quality guidelines for treated wastewater used for crop irrigationa
Category Reuse conditions Exposed Intestinal Faecal Wastewater treatment group nematodesb conforms expected to achieve the (arithmetic (geometric required microbiological mean no. of mean no. per quality eggs per 100 mlc) litrec) A Irrigation of crops Workers, <1 <1000d A series of stabilization likely to be eaten consumers, ponds designed to uncooked, sports public achieve the fields, public microbiological quality parks indicated, or equivalent treatment B Irrigation of Workers <1 No standard Retention in cereal crops, recommended stabilization ponds for industrial crops, 8-10 days or equivalent fodder crops, helminth and faecal
27 pasture and treese coliform removal C Localized None Not Not applicable Pretreatment as required irrigationf of crops applicable by the irrigation in category B if technology, but not less exposure of than primary workers and the sedimentation public does not occur Source: World Health Organization (1989). a In specific cases, local epidemiological, sociocultural and environmental factors should be taken into account, and the guidelines modified accordingly. b Ascaris and Trichuris species and hookworms. c During the irrigation period. d A more stringent guideline (<200 faecal coliforms per 100 ml) is appropriate for public lawns, such as hotel lawns, with which the public may come into direct contact. e In the case of fruit trees, irrigation should cease two weeks before fruit is picked, and no fruit should be picked off the ground. Sprinkler irrigation should not be used. f Also called drip or trickle irrigation.
2.9 PATHOGENS AND PARASITES IN WASTEWATER
Water plays a major role in mobilizing and transporting microorganisms. Rainfall washes organisms from faeces or vegetation surfaces and directs them into soils or along the land surface into surface water. Several pathogenic microbes and parasites are commonly found in wastewater, these pathogens could be bacterial, opportunistic bacterial pathogens, antibiotic producing bacteria, viral pathogens as well as protozoan parasites and helminthes.
2.9.1 Bacterial Pathogens
Faecal matter contains up to 1012 bacteria per gram which constitutes approximately 9% by wet weight of the faeces (Dean and Lund, 1981). Coliform contamination levels of vegetables are often almost the equivalent of a similar amount of fresh faeces (Keraita et al., 2003b). Wastewater bacteria have been characterized and belong to the following groups (Dott and Kamper, 1988):
• Gram-negative facultative anaerobic bacteria(e.g., Aeromonas, Klebsiella,
Esherichia,Enterobacter, And Shigella)
• Gram-negative aerobic bacteria (e.g., Pseudomonas, Flavobacterium And Acinetobacter)
• Gram-positive spore-forming bacteria(e.g., Bacillus spp)
28 • Non-spore-forming gram-positive bacteria (e.g.,Corynebacterium, Arthrobacter)
These pathogens cause enteric infections such as typhoid fever, cholera, and shigellosis. Salmonella are the most predominant pathogenic bacteria in wastewater and they cause typhoid and paratyphoid fever and gastroenteritis. Their numbers in wastewater range from few to 8,000 organisms per 100ml (Feachem et al, 1983).
2.9.2 Protozoan Parasites
The major waterborne pathogenic protozoa affecting humans are Giardia lamblia, and
Cryptosporidium. According to Dawson (2005) protozoan parasites enter the food production process via three main routes:
• Through contamination of food ingredients or raw materials on the farm;
• Through contaminated water included in the final product processing or washing, or used for
cleaning processing equipment;
• Through transfer or spread via infected food handlers or food preparers in production, food
service or domestic settings.
2.9.3 Helminth Parasites
Although helminths are not generally studied by microbiologists, their presence in wastewater, along with bacterial and viral pathogens and protozoan parasites, is of great concern in regards to human health.
The term "helminth" refers to a variety of worms that live as parasites in many species of animals and the human body. They belong to three biological categories: - trematodes (flukes), nematodes
(roundworms) and cestodes (tapeworms). Ascaris lumbricoides, Necata americanus and
Ancylostoma dueodenale and Trichuris trichura are all helminths belonging to the phylum
29 nematode (Bogtish, 1998). Their ova are excreted in faeces and spread by wastewater, soil, or food.Helminthes infection occurs when worms (or eggs) enter, mature, lay eggs and feed off a person. Helminthes infections include soil borne intestinal nematodes such as roundworm (Ascaris lumbricoides), whipworm (Trichuris trichura) and hookworm, and water borne species such as
Shistosoma haematobium and S. mansonii.
Helminthes infections affect over a quarter of the world's population, especially in the developing countries. These long-lasting parasitic infections cause widespread immune activation and dysregulation, a dominant Th2 cytokine immune profile and an immune hyporesponsiveness state
(Barkow et al., 2001). The names of the important helminthes, where they live in the human body and their geographical distribution are presented in ‘Important Helminthes in School Children’
(UNESCO media services, 2002).
They affect the health and well-being of millions of people, especially young people. About 400 million school-age children are infected by roundworm, whipworm, hookworm, shistosomiasis and other flukes and/or guinea worm. These parasites consume nutrients from the children they infect.
In doing so they bring about or aggravate malnutrition, weaken the immune system and retard children's physical and mental development.
Whipworm infections are associated with a high incidence of dysentery, chronic colitis, anaemia and growth retardation (UNESCO media services, 2001). Hookworm infections cause iron deficiency anaemia. Even minor hookworm infections can result in severe anaemia in children and in adolescent girls. Iron deficiency anaemia has been associated not only with decreased physical development, but also with decreased mental development. Helminthes infections are a leading cause of diseases among young people and adults in the world today. Helminthes infections can have a significant negative impact on school enrolment, attendance, and even the ability to learn.
30
The parasites that cause helminthes infections are naturally present in the environment. However the high prevalence of intestinal parasite infections in certain parts of the world is closely correlated with poverty and poor environmental hygiene. Most commonly, people become infected with helminthes by coming into contact with soil, water or food that contains the eggs or young worms of these parasites.
It has been successfully proven that it takes only a single helminthes egg to cause an infection in an individual (Schwartzbrod, 1998). Helminthes destroy the tissues and organs in which they live; causing abdominal pain, diarrhoea, intestinal obstruction, anaemia, ulcers, and various other health problems. If treatment is not given in time, heavy or long-term infection with various helminthes can result in death (UNESCO Media services, 2002).
Soil-transmitted helminthes (STH) infections are endemic in communities where poor environmental sanitation and poor personal hygiene are prevalent, as occurs in the majority of developing countries (Yodmani et al., 1982). Yu et al. (1993) showed that environmental pollution, sanitary condition and human behaviour play an important role in the transmission of STH infection. Yodmani et al. (1982) indicated that many sources of ascariasis from the host and in the environment such as soil in the shantytowns and vegetables sold in the market resulted in continuous active transmission of ascariasis in the area.
Another study was carried out on sewage farms, streams and vegetables to determine the sources and routes of STH infection in Sanliurfa, Turkey. Stool samples from farmhouse inhabitants as well as soil and vegetable samples from the gardens were collected and examined. In addition, water samples from streams and vegetable samples from the city market were collected and examined.
One hundred and eighty-seven (59.5%) of a total of 314 samples, including 88.4% of the stool samples, 60.8% of the water samples, 84.4% of the soil samples and 14% of the vegetable samples,
31 were found to be positive for STH eggs. These results indicate that the water, soil and vegetables are heavily contaminated, and suggest a vicious circle between humans and the environment.
Improving environmental sanitation is imperative for the control of soil-transmitted helminthiasis.
Helminthes parasites pass out of infected individuals in faeces and urine, so their numbers explode in areas where human waste is not properly managed. Fertilized eggs deposited in the soil develop rapidly and, depending on environmental conditions, may reach the infective stage within a matter of weeks (Klaas, 1987). Thereafter, eggs are transferred from soil to the vegetables then onto to hands and finally to the mouth (Kobayashi, 1999).
At a minimum, sanitary improvements required to reduce helminthes infections include: safe, efficient and hygienic management of water, safe, efficient and hygienic disposal of faeces, regular and effective use of water (with a scouring agent like soap) for hand washing after contact with stools; and hygienic food preparation methods (UNESCO media services, 2001).
All the above infections and resulting health problems can be prevented or greatly reduced through cost-effective interventions. Infections of the major intestinal helminthes can be prevented by avoiding ingestion of, or contact with, contaminated soil. Avoiding infested water greatly reduces shistosomiasis. Food safety measures help prevent fluke infections which are transmitted by meat or vegetables. Provision of safe water sources has been shown to be extremely effective in preventing guinea worm infection (UNESCO media services, 2001)
The soil-transmitted helminths are the most common and the most critical to human health. The ova are very resistant to environmental stress and to chlorination even in wastewater treatment plants
(Little, 1986). The severity of helminth infections depends on the number of worms which invaded the body from outside. This worm load also determines the rate at which infection is propagated by
32 transmission of eggs in the faeces, urine or sputum of the human host. Helminths eggs are also commonly found on such vegetables irrigated with wastewater or get transferred from the soil when it rains or during irrigation. When these contaminated vegetables are eaten raw or with inadequate cooking, the eggs burrow into the intestines and move to other sites and cause diseases. However, the survival of these organisms varies with different environmental factors e.g. low temperature which enhances the longer persistence of the pathogen on the crops.
Table 2.3 Survival times of selected excreted pathogens (helminthes) on crops
Helminths Survival time Ascaris lumbricoides 30 days Hookworm 60 but usually 30days Taenia spp/Trichuris 60 but usually less Source: (WHO, 1989; summerised by Feachem et al., 1983)
2.9.3.1 Hookworm
The hookworm is a nematode parasite that lives in the small intestine of its host, which may be a mammal such as a dog, cat, or human. Two species of hookworms commonly infect humans,
Ancylostoma duodenale and Necator americanus. The geographical distribution of these two species significantly overlaps. Necator americanus predominates in the Americas, Sub-Saharan
Africa, Southeast Asia, China and Indonesia, while A. duodenale predominates in the Middle East,
North Africa, India and (formerly) in southern Europe. Hookworms are thought to infect 800 million people worldwide.
Hookworms are much smaller than the large roundworm, Ascaris lumbricoides. The most significant risk of hookworm infection is anemia, secondary to loss of iron (and protein) in the gut.
The worms suck blood and damage the mucosa. However, the blood loss in the stools is occult blood loss (not visibly apparent).
33 They are the leading cause of maternal and child morbidity in the developing countries of the tropics and subtropics. In susceptible children hookworms cause intellectual, cognitive and growth retardation, intrauterine growth retardation, prematurity and low birth weight among newborns born to infected mothers. Hookworm infection is rarely fatal, but anemia can be significant in the heavily infected individual.
Fig. 2.1 Life Cycle and Transmission of Hookworm source:http://www.dpd.cdc.gov/dpdx
2.9.3.2 Ascaris lumbricoides
Ascaris lumbricoides, a parasitic round worm causes Ascariasis a debilitating human disease.
Perhaps as many as one quarter of the world's people is infected, and ascariasis is particularly prevalent in tropical regions and in areas of poor hygiene. Other species of the genus Ascaris are parasitic and can cause disease in domestic animals.
Infection occurs through ingestion of food contaminated with fecal matter containing Ascaris eggs.
The larvae hatch, burrow through the intestine, reach the lungs, and finally migrate up the respiratory tract. From there they are then reswallowed and mature in the intestine, growing up to
34 30 cm (12 in.) in length and anchoring themselves to the intestinal wall. Infections are usually accompanied by inflammation, fever, and diarrhea, and serious problems may develop if the worms migrate to other parts of the body.
Roughly 1.5 billion individuals are infected with this worm. Ascariasis is endemic in the United
States, China, Ozark Mountains; Southeast Asia, central Africa and the coastal regions of the West
Africa.
Ascariasis sources can often be measured by examining food for ova. In one field study in
Marrakech, Morocco, where raw sewage is used to fertilize crop fields, Ascaris eggs were detected at the rate of 0.18 eggs/kg in potatoes, 0.27 eggs/kg in turnip, 4.63 eggs/kg in mint, 0.7 eggs/kg in carrots, and 1.64 eggs/kg in radish (Habbari et al, 1999). A similar study in the same area showed that 73% of children working on these farms were infected with helminths, particularly Ascaris, probably as a result of exposure to the raw sewage.
Roundworm infections can retard growth. They decrease the absorption of nutrients that the body needs to grow. They cause structural problems in the small intestine in children and are thought to be a cause of frequent or serious pulmonary disease among children. Intestinal obstructions frequently result in the hospitalization of children. Death is common in children when worms move to organs outside of the intestines such as the trachea, liver, and heart, or when complications occur.
35
Fig. 2.2 Life Cycle and Transmission of Ascaris lumbricoides source:http://www.dpd.cdc.gov/dpdx
Adult worms (1) live in the lumen of the small intestine. A female may produce approximately
200,000 eggs per day, which are passed with the feces (2). Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks (3), depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed (4), the larvae hatch, (5) invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs. The larvae mature further in the lungs (6) (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed (7).
Upon reaching the small intestine, they develop into adult worms (8). Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.
2.9.3.3 Strongyloides stercoralis
36 This 2 mm-long worm is found both free-living in soil, and as a parasite of humans, other primates, and dogs. The free-living male and female worms are not infectious; however, their offspring all develop to infectious larvae. These infectious larvae penetrate the skin when there is contact with the soil. Some of them enter the superficial veins and ride the blood vessels to the lungs, where they enter the alveoli. They are then coughed up and swallowed into the gut, where they parasitise the intestinal mucosa (duodenum and jejunum).There, they reach sexual maturity and produce eggs (all infectious larvae are female and thus all parasitic adults are females). The eggs hatch in the intestine and young larvae are then excreted in the feces. It takes about two weeks to reach egg development from the initial skin penetration. By this process, S. stercoralis can cause both respiratory and gastrointestinal symptoms. Adult worms can live up to a year in dogs.
Autoinfection can also occur when the larvae which hatch from the eggs in the small intestine have time to mature to infectious larvae before being excreted. They penetrate the wall of the lower ileum or colon or the skin of the perianal region; enter the circulation again, up to the lungs, and back down to the small intestine thus repeating the cycle. Because of autoinfection, humans have been known to still be infected up to 50 years after they were first exposed to the parasite.
Immunosuppressive drugs, such as those used for tissue transplantation, (especially corticosteroids) can increase the rate of autoinfection to the point where there is an overwhelming number of larvae migrating through the lungs, and in many cases this can prove fatal. While there are a number of drugs which will kill the adult worms, these drugs have little effect on the majority of these auto infective larvae during their migration through the body.
37
CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 STUDY AREA
Kumasi is the second largest and one of the fastest growing urban cities in Ghana with an estimated population of 1.2 million and an annual growth rate of 2.6% (Ghana Statistical Service, 2000). It lies between latitude 6° 42 North and longitude 1°35 West and an altitude of 287m. It covers a total area of 57sq.m and the topography of the region varies from gently undulating to distinctly hilly and mountainous (Taylor, 1982). The region has two major seasons, the rainy and dry seasons. The rainy season experiences major rains between March and July and minor rains between September and November with an annual rainfall of about 1300mm. The relative humidity ranges between
1270 to 1410 mm with average daily sunshine durations ranging between 2 to 7 hours and daily minimum and maximum temperatures of 21.20°C and 35.50°C, respectively (Meteorological
Services Department, Kumasi Airport Weather Station, 2002)
Kumasi’s unique position and availability of infrastructure coupled with the large markets have made it the hub of trade in the Ashanti region. The Kumasi Central Market, one of Africa’s largest markets is in the region. Other markets including the Asafo market, the second largest in the region and the European market receives thousands of people daily.
The study was conducted on selected vegetable production (farms) sites, vegetable selling markets and street food vendor sites in and around Kumasi.
38
Figure 3.1 Map showing Kumasi in relation to the rest of Ghana
3.2 RESEARCH METHODS
39 3.2.1 Sampling sites
3.2.1.1 Production (Farm) Sites:
Three production (farm) sites, two urban (Karikari and Badu farms) and one peri-urban farm at
Deduako were selected for the study (Fig.3.2)
Figure 3.2: Map of Urban/Peri Urban Vegetable Farm Sites in Kumasi and Selected Study Farms in Green Colour
SITE 1: KARIKARI FARM
Karikari Farm is located close to Gyenyase, an urban suburb of Kumasi. It covers a total area of
3ha with 2.8ha being irrigated and an average bed size of 14sq.m. The land, which is in a low land area, belongs to the Chief of Gyenyasi. Although the farm is close to a stream, farmers do not use it for irrigation but rather obtain water from shallow wells dug at designated points on the farm and channeled along the ridges of the vegetable beds. Irrigation is done by means of watering cans.
40 Crops grown on this farm include cabbage, lettuce, green pepper, cassava and plantain.
Plate 3.1: A section of Karikari Farm with some areas developed for residential use.
SITE 2: BADU’S FARM
Badu’s Farm is located at Gyenyase and is close to Kwame Nkrumah University of Science and
Technology (KNUST) main sewerage treatment plant which is about 1km away from the university campus. The land which is owned by KNUST, covers a total area of 12.7ha with 10.3ha being irrigated and has an average bed size of 14sq.m. Farmers obtain irrigation water from shallow wells dug along the ridges of the beds and at designated points on the farm; irrigation is done by means of watering cans. Types of crops grown include lettuce, cabbage, spring onions, green pepper and carrots.
41
(a)
(b)
42 Plate 3.2 (a&b) Sections of the Badu farm site
SITE 3: DEDUAKO
The peri-urban farm at Deduako is located 10km from the centre of Kumasi. The farm lies in a low land area with water available all year round. It covers a total area of about 10ha with 9.3ha being irrigated. Crops grown include lettuce, cabbage, spring onions and carrots. Irrigation is mainly overhead with motorized sprinkler using water from an impounded stream running close to the farm.
Plate 3.3: A section of the Deduako farm site.
3.2.1.2 Market Sites
Three market sites where produce from the selected study farms are sold were identified as part of the study. Produce from Karikari’s farm were traced to the Railway market, those from Badu’s farm
43 to the European market and French line and produce from Deduako were traced to the Asafo market. Three sellers were selected from each market site for the study.
3.2.1.3 Street Food Vendor Sites
The Kumasi Metropolitan Authority is divided into four sub-metros for ease of administration.
Based on these divisions, five areas (Stadium, Oforikrom, Dichemso, Krofrom and Tech-Junction) were randomly selected for the study. Fifteen street food vendor sites that purchase lettuce from the selected study market sites were selected from these areas and included in the study.
3.2.2 Sampling
Sampling was done between June and December, 2005 and between February and June, 2006 at all the selected farms, markets and street food vendor sites.
A total of 321 samples were analysed. Out of this number was 162 lettuce samples from all three production(farm) sites ( 54 lettuce heads per farm site), 90 lettuce heads from markets selling produce from the selected farm sites ( 27 from railways, 27 from Asafo and 36 from European and
French line markets), 30 lettuce samples from selected street food vendors, 21 irrigation water samples from the selected farms (9 from Karikari, 9 from Badu and 3 from Deduako) and 18 refreshing water samples from Railways and European/French line markets. Sellers at Asafo market displayed lettuce without refreshing water.
3.2.2.1 Lettuce Sampling from Production (Farm) site
On each sampling date, three lettuce heads per bed were randomly harvested from six beds under cultivation per farm site by means of a sketch map and placed separately in labeled sterile plastic bags.
44
Plate 3.4: Sampling of lettuce from a bed at one of the selected farm sites
3.2.2.2 Market
From each market seller, three lettuce heads were collected around mid-day to ensure that the lettuce had experienced some splashing/refreshing with water. Each was placed separately in separate labeled plastic bags.
3.2.2.3 Street Food Vendors
From each street food vendor site, about 120g of already prepared and sliced lettuce were collected and placed in labeled food bags.
3.2.2.4 Irrigation/Refreshing Water Sampling
On each sampling date, irrigation water samples from either the hand dug shallow wells or streams on the farms were collected using one litre Duran Schott bottles. The bottles were dipped into the
45 water without opening until it was about 30cm below the water surface. The bottle was then opened and filled; the cap was replaced under the water and tightened.
Samples of splashing/refreshing water used for the lettuce by the sellers in the market were also taken aseptically from the selling receptacles using sterile one liter Duran Schott bottles.
All samples (lettuce, irrigation and refreshing water) were transported to the laboratory in an ice chest containing ice packs and analysed for protozoan parasites and helminth eggs within 24hours.
3.2.3 Preparation of Samples and Quantification of Helminth Eggs
One hundred grams of lettuce was washed under running water into a bowl, and then transferred into a sterile container. The water was allowed to settle in a 2 litre container for 3hours or overnight.
As much supernatant as possible was sucked up using a vacuum pump and the sediment placed into tubes and centrifuged for 3 min at 400g. The supernatant was poured off and the sediment resuspended with Zinc Sulphate of 1.3 densities and homogenized with a spatula. It was again centrifuged for 3 min at 400g. The Zinc Sulphate supernatant was poured into a fresh 2 litre bottle and diluted with 1 litre of water. The container was allowed to stand for 3 hours or overnight. As much supernatant was sucked up and the sediment resuspended by shaking and emptied into centrifuge tubes, the bottle was rinsed twice with deionized water and placed into the tubes with the sediment. The tubes were centrifuged for 3min at 480g. The sediments were regrouped into one tube and centrifuged again for 3min at 1600 rpm. The sediment was again resuspended in about 5ml acid/alcohol (H2SO4+C2H5OH) buffer solution and 2ml ethyl acetate solution. It was shaken and occasionally opened to let out gas. It was then centrifuged for 3min at 660g. Much of the supernatant was sucked up leaving less than 1ml of liquid. The deposits were read on a slide using a light microscope.
The number of eggs per liter was calculated from the equation:
N = AX/PV
46 Where N = Number of eggs per liter of sample
A = Number of eggs counted in the slide or mean counts from two or three slides
X = Volume of the final product (mL)
P = Volume of the slide (mL)
V = Original sample volume (L)
3.2.4 Identification of Helminth Eggs
The helminth eggs were identified on the basis of their shape and size and compared with standard eggs on chart (WHO, 1996). The counting was done under a light microscope in both chambers of a haemocytometer.
3.2.5 Health Risk Assessment and Perception
Risk and perception were assessed using structured questionnaires, focus group discussions and an observation check lists at all stages of sampling (farm sites, markets and street vendor sites) to document prevailing hygienic practices. The specific health risks examined included irrigation practices, Personal Protective Equipment and processing procedures (handling, washing, serving, and preservation of leftovers).
3.3 STATISTICAL ANALYSIS
The statistical package for Social Scientists (SPSS) version 11.0 was used for testing the various statistical relationships between and within variables.
47 CHAPTER FOUR
4.0 RESULTS
4.1 HELMINTH EGGS IN IRRIGATION WATER AND LETTUCE LEAVES AT PRODUCTION SITES
Morphological features of the different helminth eggs contained in the irrigation water samples from the different farm sites suggest that they are mostly, Ascaris lumbricoides, Shistosoma,
Hookworm, Trichuris trichura, Taenia, Clonorchis and Strongyloides larvae (Table 4.1).
Table 4.1 Description of helminth eggs/larvae associated with wastewater irrigated vegetables
WHO Description (Size, shape and Sample Description Probable colour) identification The fertile eggs are oval to round, 55µm The eggs were brown in Ascaris to 75µm by 35µm to 50µm wide with a colour and oval/round in lumbricoides thick lumpy outer shell (mammillated, shape, measuring 50µm to uterine, or proteinatious layer) that is 60µm in length and 35µm to contributed by the uterine wall. There is 45 µm in width and having a one cell inside the egg which is separated thick lumpy outer shell. There from the shell at both ends. When the was one cell inside the egg eggs are passed out in faeces they are which is separated at both golden yellow to brown in colour. The ends. Most of the eggs had egg has a conspicuous mamillations on conspicuous mamillations on its outer surface. Sometimes, normal their outer surface but few fertile eggs lack the mamillated layer and lacked the mamillated layer. are referred to as “decorticated” eggs. (Plate 4.3) The infertile eggs are elongated, much larger in size measuring 85-95 by 43 to 47µm wide. They have thin shells and grossly irregular mamillated layer, content of the egg is usually granular and lacks organization. These measure 50 to 55 by 22 to 24µm. These eggs were elongated Trichuris They are elongated and lemon shaped and lemon shaped with trichura
48 with a brown, smooth shell, bipolar smooth outer shell and bipolar prominences (plugs) at each end. At the plugs at each end. They time the egg is laid, it contains a single- contained single-cell ovum cell ovum These eggs are characteristically barrel- The eggs were colourless Hookworm shaped with a thin, hyaline shell; they barrel-shaped with thin, measure 65 to 75by 36 to 40µm. The egg hyaline shell containing is colourless with greyish cells. They are greyish cells in the 8 cell usually in the 4 to 8 cell stage in faeces or stage. in a more advanced stage of cleavage in samples that have been kept at room temperature for even a few hours
These have a size of 112 to 170µm by 50 These measured from 115 to Shistosoma to 70µm. It is elongated with rounded 130µm in length and 55 to haematobium anterior end and a terminal spine at the 60µm in width. the eggs were posterior end. It is embyonated and elongated and rounded at the contains a matured miracidium anterior end with a terminal spine at the posterior end. they contained miracidia (Plate 4.1)
The first-stage rhabditoid larvae The larvae measured 150 to Strongyloides measures 180 to 380µm by 14 to 20µm. 250µm in length and 14 to stecoralis The larvae have a short buccal capsule, 18µm in width. It had a an attenuated tail and a prominent genital conspicuous buccal capsule, primordium an attenuated tail and a prominent genital primordium.(Plate 4.2) The eggs are all identical, i.e. 31 to 43µm The eggs were all identical, Taenia spp in diameter, with a thick, prismatic- with thick walls, containing appearing shell wall, and contain a 6- hooked embryo with a hyaline hooked embryo, the oncoshpere. membrane around the eggs. Occasionally a thin, hyaline primary embryonic membrane may be retained around the eggs
49 The eggs are 27 to 35µm by 12 to 19µm. The eggs were smaller Clonorchis they have a seated operculum and usually compared to the others. They a small protuberance at the opposite end. were cup-shaped with The shell may have minute adherent operculum and small debris. Eggs from faecal origin contain a protuberance at the opposite miracidium end. They usually had adherent debris.
Plate 4.1 Larvae of Strongyloides stecoralis (low and high magnifications)
Plate 4.2 Shistosoma haematobium Plate 4.3 Ascaris lumbricoides
50 Irrigation water sampled from Karikari, Badu and Deduako farms contained Helminths with mean
total egg/larvae counts of 3, 25 and 3 eggs l-1, respectively (Table 4.2). There were no statistically
significant differences between Karikari and Deduako farms (P =0.215) but there were significant
differences between Karikari and Badu (P ≤ 0.001) and between Badu and Deduako (P ≤ 0.001).
Ascaris lumbricoides eggs were contained in all the irrigation water samples examined and had the
highest numbers ranging between mean counts of 2-17 eggs l-1 compared to 0-4 larvae l-1 for
Strongyloides, 0-1 eggs l-1 for Shistosoma and 0-1 eggs l-1 for Trichuris trichura. However, Taenia,
Hookworm and Clonorchis ranged between 0-1 eggs l-1 for water samples (Table 4.2) (Figure 4.1).
Table 4.2 Types and population densities (per litre) of helminth eggs in Irrigation water for lettuce production and on lettuce leaves (per 100 g) in three sites in Urban Kumasi
Mean Farm total sampling egg site Strongyloides1 Ascaris Shistosoma Hookworm Trichuris Taenia Clonorchis count
Karikari 1(1) 2(4) 0(0) 0(0) 0(0) 0(0) 0(0) 3(5) farm Badu's 4(1) 17(12) 1(0) 1(0) 1(0) 1(1) 0(0) 25(14) farm Deduako 0(1) 3(3) 0(0) 0(0) 0(0) 0(0) 0(0) 3(4) farm
Figures in parenthesis represent mean numbers of eggs/larvae on lettuce leaves
1 These were larvae and not eggs
N for Lettuce =54 for all farm sites; n for Irrigation Water samples = 9 for Karikari and Badu farms and 3 for Deduako
farm
Similarly, mean counts of helminth eggs on lettuce samples from the selected farm sites were high
recording 5, 14 and 4 eggs 100g-1 wet weight for Karikari, Badu and Deduako farms, respectively
(Table 4.2). These differences between the Badu and Karikari farms and between Badu and
Deduako were statistically significant (P ≤ 0.001) but differences between Deduako and Karikari,
51 were not statistically significant (P = 0.444). Ascaris lumbricoides eggs on lettuce leaves were also high in all the three farm sites studied with a mean range of 3-12 eggs 100g-1. However,
Strongyloides varied from 0-1 larvae 100g-1 and Taenia between 0-1eggs 100g-1 wet weight (Table
4.2) (Fig. 4.2).
Considering helminth egg population in irrigation water samples from all the three farms, percentage numbers in Badu’s farm were highest, 81.3% (25 eggs l-1), followed by Deduako, 9.9%
(3 eggs l-1) and Karikari, 8.8% (3 eggs l-1). In all the farms, Ascaris lumbricoides eggs dominated with population density of 75%, 69% and 89% and Strongyloides larvae were least prevalent with
25%, 19% and 11% of the total helminth egg numbers counted on Karikari, Badu and Deduako farms, respectively. Other helminthes eggs identified on samples from Badu’s farm included
Shistosoma (3.2%), Hookworm (2.9%), Trichuris trichura (2.7), Taenia spp (2.7%) and Clonorchis
(0.5%).
The percentage of helminth eggs on lettuce leave samples were similarly high, 58% (14 eggs 100g-
1) in Badu, 22% in Karikari (5 eggs 100g-1) and 20% in Deduako (4 eggs 100g-1). Numbers of
Ascaris lumbricoides eggs were also high on the lettuce leaves from all the three farms recording
74% in Karikari, 82% in Badu and 60% for Deduako.
The variety of helminth eggs observed in irrigation water from Badu’s farm was wider (Ascaris lumbricoides, Strongyloides, Shistosoma, Hookworm, Trichuris trichura, and Taenia) compared to
(Ascaris lumbricoides and Strongyloides) in Karikari and Deduako (Figure 4.1). Similarly, helminth eggs on lettuce leaves also varied widely on Badu’s farm (Ascaris lumbricoides, Strongyloides,
Shistosoma haematobium, Hookworm, Trichuris, Taenia, Clonorchis) compared to Karikari
(Ascaris lumbricoides, Strongyloides, Shistosoma haematobium, Trichuris, Taenia) and Deduako
(Ascaris lumbricoides, Strongyloides, Shistosoma haematobium, Hookworm, Trichuris) (Fig 4.2)
52 20
l 15
Strongyloides
Ascaris 10 Sh ist o so m a
Hookworm
Trichuris Mean Number of eggs/ of Number Mean 5 Taenia
Clornochis
0 Karikari Badu's Deduako Farm Farm farm samplng sites
Figure 4.1: Helminth eggs/larvae in irrigation water samples from the farm sites.
20
15 Strongyloides Ascaris
Shistosoma
10 Hookworm
Trichuris
Taenia
5 Clornochis Mean Num eggs ber of /100g weightwet
0 Karikari farm Badu's farm Deduako farm sampling site
Figure 4.2: Helminth eggs/larvae on lettuce samples from the farm sites.
53 4.2 HELMINTH EGGS IN LETTUCE AND REFRESHING WATER FROM SELECTED MARKET SITES
Mean helminth eggs/larvae numbers on lettuce samples studied were 6, 7, and 2 eggs/100g wet weight from Railways, European/French Line and Asafo market sites, respectively (Table
4.3).There was no statistical difference (P =0.652) between the Railway market and the
European/French Line market but the differences between the Railway and Asafo Market, and between Asafo market and European/French line markets, were statistically significant (P ≤ 0.001).
Similarly, mean helminth eggs counts in refreshing water samples were 4 for Railways and 15 for
European/French line markets (Table 4.3) and this difference was statistically significant (P ≤
0.001).
Compared to farm samples, most of the helminth eggs counted on lettuce leaves and in refreshing water in the markets were Ascaris lumbricoides with mean range of 1 to 6 eggs 100g-1 wet weight for lettuce leaves and 4 and 10 eggs l-1 for refreshing water (Table 4.3).
Table 4.3 Types and population densities (per litre) of helminth eggs in refreshing water for lettuce and on lettuce leaves (per 100 g) in three Market Sites in Urban Kumasi
Mean Market total sampling egg site Strongyloides1 Ascaris Shistosoma Hookworm Trichuris Taenia Clonorchis count
Railways 1(0) 5(4) 0 0 0 0 0 6(4)
European/ French 1(4) 6(10) 0 0 0(1) 0 0 7(15) Line
2 Asafo 1 1 0 0 0 0 0 2
Figures in parenthesis represent mean numbers of eggs/larvae in refreshing water 1 These are larvae and not eggs N for lettuce =27 for
54 Railways and Asafo Market and 36 for European/French Line market. N for refreshing water samples = 9 for Railways and 12 for European/French line 2Asafo Market displays lettuce leaves without refreshing water.
Eggs of Ascaris lumbricoides were counted on almost all lettuce samples but represented 70% of all helminth eggs counted on lettuce from Railways (2-10 eggs 100g-1 wet weight), 78% from
European/French Line samples (2-11 eggs 100g-1 wet weight) and 60% from the Asafo market (1-4 eggs 100g-1 wet weight) samples.
Similarly, helminth egg numbers in refreshing water were predominantly Ascaris lumbricoides and were 24% in the Railway samples ranging from 1 to 9 eggs l-1, 76% in European/French Line samples ranging from 4 to 25 eggs l-1.
There were no statistically significant differences in helminth egg numbers on lettuce between the
Railway market and European/French line markets (P =0.652) but in the refreshing water, these differences were statistically significant (P ≤ 0.001).
The variety of helminth eggs observed in Refreshing water from the European/French line markets was wider (Ascaris lumbricoides, Strongyloides, Shistosoma, Trichuris trichura, Clonorchis and
Taenia) compared to (Ascaris lumbricoides, Shistosoma, Taenia and Strongyloides) detected in samples from the railway market (Figure 4.3). Similarly, helminth eggs on lettuce leaves also varied widely on samples from the European/French line markets compared egg types detected on lettuce samples from the Railway and Asafo markets (Fig 4.4)
55 10
Strongyloides
Ascaris
Shistosoma
5 Hookworm
Trichuris
Taenia
Mean Number of Eggs/l of Number Mean Clornochis
0 Railways EU.MKT+FR LINE Asafo Sampling Site
Figure 4.3: Helminth eggs/larvae in refreshing water samples from the market sites.
10 t
Strongyloides
Ascaris
Shistosoma 5 Hookworm
Trichuris
Taenia
Clornochis Mean no. of Eggs/100gweigh wet
0 Railways EU.MKT+FR LINE Asafo Mkt Sampling Site
Figure 4.4: Helminth eggs/larvae on lettuce samples from the market sites.
4.3 RELATIONSHIPS BETWEEN HELMINTH EGGS/LARVAE COUNTS IN IRRIGATION WATER, FARM LETTUCE, REFRESHING WATER AND MARKET LETTUCE
56
Helminth egg counts on lettuce leaves from Karikari and Deduako farms was 25 to 36% more than counts from the irrigation water used. However, in Badu farm helminth egg numbers were 25% more in irrigation water compared to that on lettuce leaves (Fig.4.5). Comparing the numbers of helminth eggs on lettuce leaves and in irrigation water between the different farms, revealed weak positive correlations (r) of 0.437 for Karikari, 0.268 for Badu and 0.048 for Deduako.
In the same way, the population density of helminth eggs on lettuce leaves samples was 20% more on lettuce leaves on Railway market compared to the refreshing water used. However, the population counted from the European/French Line markets where 26% more in the refreshing water (Fig 4.6). A weak positive correlation exists between the lettuce leaves and refreshing water samples (r =0.285) for Railways and (r =0.211) for the European/French Line markets.
Along the production - market chain, helminth egg numbers either reduced or increased. From the
Karikari farm to the Railway market, egg counts increased by 10.5% but from the Badu’s farm to the European/French line markets they decreased by 33.3%. Egg numbers also decreased by 42.9% for produce from Deduako farm to the Asafo market (Fig 4.7).
57 30 30
25 25
20 20
15 15
10 10 Total Egg Count / l / Egg Count Total
5 5
Mean Total Egg Count/100g wet weight Egg wet Count/100g Mean Total 0 0 KARIKARI BADU DEDUAKO Sampling Sites irrigation water (S.E 2.7) lettuce leaves( S.E 3.6)
Figure 4.5: Mean total count of helminth eggs on lettuce leaves and in irrigation water
20 18
18 16
16 14
14 12 12 10 10 8 8 6 6 Mean Total Egg Total Egg Count/l Mean
4 4 Mean Total Egg Count/100g Wet Weight Wet Count/100g Egg Total Mean 2 2
0 0 RAILWAYS EU.+FR. LINE ASAFO Sampling Sites
Lettuce leaves(S.E 1.6) Refreshing water(S.E 1.9)
Figure 4.6: Mean total count of helminth eggs on lettuce leaves and in refreshing water
58 20 t 18
16
14
12
10
8
6
4
ean no. of helminth eggs/100g wet weigh 2 M 0 123Farms Sampling sites Markets
1: Karikari Farm –Railway Market, 2: Badu Farm – European/French line Market 3: Deduako Farm-Asafo Market
Figure 4.7: Total helminth egg count on lettuce leaves on farm and their corresponding markets
4.4 HELMINTH NUMBERS AT STREET FOOD VENDOR SITES
Sliced lettuce leaves sold as part of most ready to eat street foods were also found to carry helminth eggs. Mean counts were 2, 3, 1 and 2 eggs 100g-1 wet weight (Table 4.4) for Stadium, Krofrom,
‘Tech Junction’ and Dechiemso, respectively. Ascaris lumbricoides and Shistosoma haematobium were the two main microbial contaminants in all the samples analysed (Table 4.4) but the differences were not statistically significant (P =0.47). The total population density of helminth eggs on lettuce samples from Stadium ranged from 1 to 4 eggs 100g-1, Ascaris lumbricoides varied from 0 to 1 egg 100g-1 while Shistosoma ranged between 2 and 3 eggs 100g-1. Lettuce samples from
Krofroum recorded the highest counts of helminth eggs with the total population density ranging from 1 to 7 eggs 100g-1 with both Ascaris and Shistosoma recording a range of 1 to 4 eggs, respectively. The trend was no different from ‘Tech Junction’ and Dichemso where the population density range was from 1 to 3 eggs 100g-1wet weight, Ascaris lumbricoides and Shistosoma ranged from 0 to 1 and 1 to 2 and from 1to 2 and 0 to 1, respectively.
59 Table 4.4 Mean number and types of helminth eggs on lettuce leaves (per 100g) from selected street food vendor sites. Ascaris Shistosoma Mean total egg Street food vendor site lumbricoides haematobium count (range) (range) Stadium 0 – 1 0 – 3 2
Krofrom 1 – 4 1 – 4 3
Tech Junction 0 – 1 1 – 2 1
Dichemso 1 – 2 0 – 1 2 n for lettuce samples =4 for Stadium, 6 for Krofrom, 3 for ‘Tech Junction’ and 2 for Dichemso
4.5 HEALTH RISK ASSESSMENT
4.5.1 Production Site
Farmers from all the three selected sites were males with most of them living close to their farms.
Each of the studied vegetable production farms had an average of fifteen farmers who were all producing mainly for sale.
During informal Focus Group Discussions, all the farmers admitted having experienced some health problems in the last one year. Some attributed this to their exposure to wastewater. Although most of the farmers acknowledged the risk posed by wastewater use in irrigation, 80% also indicated their health problems could also be due to pesticides and poultry manure use. Farmers mostly reported of malaria (95%), skin and foot rot diseases (50%); diarrhoea (10%) with other complaints being back ache. Although some farmers had family members with similar health problems, they did not attribute this to the consumption of their produce or exposure to wastewater.
During sampling, observed unhygienic practices on the farms included the disposal of waste in irrigation water channels, farmers walking indiscriminately through the irrigation water channels without any Personal Protective Equipment (PPE), washing of their body parts in the dug-wells after the day’s work (Plate 4.3).
60
Plate 4.3: Farmer working without Personal Protective Equipment
4.5.2 Market Sites
All sellers interviewed at the markets were females and retailers of lettuce and other exotic vegetables. Sixty three percent (63%) of the sellers displayed their produce in receptacles with water for refreshing the produce from time to time to keep them fresh.
Although most of the sellers did not associate any health risk with their produce they admitted the source of irrigation water and the pesticides used could lead to cholera and other diarrhoeal diseases. Some of the possible causes of contamination on the markets could be the practice of washing different types of vegetables in the same bowl of water and the use of refreshing water for other activities as washing of hands before and after eating. The surrounding vegetable market environment on the markets was unclean.
4.5.3 Street Food Vendor Sites
61 Sixty-three percent of the street food vendors were between the ages of 21-30 years, 79% were females and 21% males. Seventy-nine percent had either primary or secondary education, and twenty-one percent had no formal education.
In getting rid of soil particles on their produce, 96% of the sellers washed/cleaned their lettuce with pipe borne water and 4% with well water. 49% of the sellers added salt and 13% added vinegar to the washing water because it could kill pathogens present on the produce. Others simply do that to impact flavour (which some of their customers like) to the lettuce. But most of them prefer salt because claimed it is cheaper and easy to get (Fig. 4.8).
38%
salt
49% vinegar
no additive
13%
Figure 4.8: Types of sanitizing solutions used by street food vendors for washing lettuce
62 CHAPTER FIVE
5.0 DISCUSSION, CONCLUSION AND RECOMMENDATION
5.1 DISCUSSION
5.1.1 Contamination of Irrigation Water and Lettuce at Production Sites
The study shows that lettuce leaves produced, sold and consumed (from “farm to fork”) in urban and peri-urban Kumasi were contaminated with helminths eggs; with the helminths loading decreasing from 4 to 14 eggs 100g-1 wet weight on farm to 2 to 15 on market and 1 to 3, on the chopped lettuce leaves sold by street food vendors (Tables, 4.2, 4.3 and 4.4). Helminth eggs numbers on farms sampled in this study were much higher compared to work by Ozlem and Sener,
(2005) who reported between 1 to 3 eggs on farms studied in Turkey. The difference could be due to the quality of the irrigation water being used by the vegetable and fruit farmers in Turkey.
In our study however, the quality of the irrigation water on the three farm sites were low recording between 3 and 25 helminths eggs/l, exceeding by far the recommended level of <1 egg l-1 for unrestricted irrigation (WHO, 1989) and which could account for the higher numbers on the leaves.
Amoah et al. (2005) recorded between 2 to 4 eggs l-1 in some irrigation water sources in Kumasi and Accra while Cornish et al. (1999) earlier reported between 1 and 5 helminths eggs l-1 in both urban and peri-urban irrigation water sources including shallow wells. In Metropolita